Every once in a while while the engine is idling, usually cold. The engine shudders for a moment, kind of like a random misfire. No CEL on, I'm thinking plugs and wires might be the culprit, I know the serp belt needs to be replaced too since it squeaks when it's cold idling. Any thoughts?

 

IAC port need a cleaning? as well as right behind butterfly in TB.
probably not the belt squeaking more like one of the pulleys. or is it a squeal?

 

If the plugs and wires are old...
That's why it's called preventative maintenance. Maintain it to help prevent a problem.